KR950012849B1 - Method for the use of gas assistance in the molding of plastic articles - Google Patents

Abstract

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Description

[Name of invention]

How to Use Gas Aid in Molding Plastic Products

[Brief Description of Drawings]

1 is a process flow diagram showing the operational steps of the novel molding process of the present invention;

FIG. 2 is a schematic of the molding sample full length name presented in relation to the process steps of FIG. 1;

3 is a side view of the bullbous tang and lens cover of FIG. 2;

4 is a cross-sectional view of a molding in which first and second filling of pressurized gas is used to form a structure;

FIG. 5 is a cross sectional view taken along line 5-5 of FIG. 4, illustrating the cavities formed in the molding and the gas pin at its gas injection position;

6 is a sectional view taken along line 6-6 of FIG. 4;

7 is a sectional view taken along line 7-7 of FIG. 4;

8 is a partially enlarged sectional view in which the gas pin of FIG. 5 is separated;

9 is a partial cross-sectional view of yet another embodiment of the present invention in which a second fill of pressurized gas is directly injected into the forming space and the gas fin is in its gas injection position;

FIG. 10 is a figure similar to that of FIG. 9 except that the gas pins are backed out to distribute the molding.

Detailed description of the invention

[Technical Field]

The present invention relates to a method of plastic injection molding, and more particularly, to a method of using pressurized gas to assist the molding process.

[Background]

It is believed that the use of pressurized gas to aid the conventional plastic injection molding process was first commercially feasible by the invention of Friedrich, published in US Pat. No. 4,101,617, issued July 18, 1987. Friedrich's patent pointed out the problem of molding hollow shaped bodies in a single injection molding operation, simultaneously with the injection of the molten plastic resin into the artcle-definig cavitr. , Or immediately after, how to introduce compressed gas. Furthermore, the Flyderich patent has described the relationship of depressurizing or relieving molded articles by nozzle separaration. Friedrich's early work was in the formation of practical items such as clean interior and exterior materials. Recently, the patented Friedrich method has been applied to the molding of hollow plastic products of various shapes and sizes.

In the early days, the use of tidal pressurized gas in conventional plastic extrusion processes was not recognized for all of the functional attributes known to be enjoyed today. Moreover, during its early years, as a special process for forming products of relatively thick cross-section, which are light in weight and have a favorable surface finish, i.e., avoiding sink marks associated with conventional plastic injection molding, The focus was more on the use of foam (structua1 foam). However, due to certain defined inherent features of the process, the range of potential adaptations of structural foam molding of thermoplastic materials has been limited. Among these properties are the relatively long molding time required for cooling the plastic in the mold (bubbles act to insulate heat conduction) and the surface finish associated with the molten plastic resin, which caused the foam to come into contact with the cold surface wall of the molding space. There was a problem of (outward spreading, blistering and twisting).

In recent years, interest has returned to the use of gas assistance to assist conventional plastic injection molding to achieve the quality and productivity expected of structural foam molding. Surface quality, lower clamp tonnage, rapid molding time, weight reduction, material savings and minimization of partial distortion or warpage can all be achieved with the proper use of gas assisting in conjunction with conventional plastic injection molding processes. Dr. Ken C. Rusch's paper under the Gas Assisted Injection Molding-The New Thermoplastic Molding Technology For Exterior Body Panele, proposed at the 1989 meeting of the American Association of Automotive Engineers on March 2, 1989, The relevant history of the use of the is discussed in great detail.

The stimulus to the present invention was the inventor's research to realize the successful plastic injection molding of automotive headlight covers. This type of cover elevates the aesthetic and aerodynamic design of the car by pivoting between the open position revealing the hidden headlight lens and the closed position concealing the light lens. The configuration of the headlight cover consists of a substantially flat plate intended to appear coplanar with the body plate of the front end when the cover is in the closed position. The plate section is mounted by a pair of flange arms integrally joined to opposite ends. Each flange arm extends at right angles to the substantially flat cover portion.

The object of the inventors was to realize a headlamp cover as a plastic molded part to replace the conventional die cast metal parts. Die-cast metal parts are relatively heavy, requiring a high rated motor or actuator to move the drying lamp cover between its open and closed positions. In addition, diecast covers have thermal cycling problems and cannot withstand the passage of factory paint ovens, where temperatures may reach or exceed 400 ° F without experiencing permanent deformation. Die-cast metal parts have the disadvantage of requiring a second, off-line facility, which adds to the cost and complexity of automated vehicle assembly.

There have been some practical problems facing the inventor in realizing a cover design, such as a roll of plastic molding bias. First, the outer surface of the substantially flat part of the headlight cover must be of "A-class" quality and be able to be painted on an automated line. Due to the incompleteness of the sink mark grooves or rudder, any surface deradation was difficult to accept due to commercial standards. Second, the headlight cover is nothing but the microscopic smoothness of the surface and not bent or twisted across its substantially flat surface. Third: The dimensional integrity of the flange arm was critical to ensure safe and integrated mechanical operation when the headlight cover was operated between its closed and open positions. Fourth, the parts had to be filled. In other words, the part design had to be such that the resin could be filled at a processing temperature that does not cause sensibility of the resin composition, and at injection pressures that do not produce a resin shear force that would reduce the mechanical strength of the regular production standard and the finished product. The parts have been molded in conventional plastic injection molding processes on a standardized development basis with the desired success.

The dilemma facing the inventor can be frankly expressed as follows. (i) Too low plastic injection pressure used to pose a risk of inferior surface quality and non-filling of fragments; (ii) Too high injection pressure or injection speed, or both, was deformed due to the risk of molecular shear of the material. Used to cause molded-in srewss exposed by lack of strength and strength; (iii) Too high a resin temperature reduces the viscosity of the molten resin, which is just a risk of exceeding the material processing temperature and has led to material sensitization and inhomogeneization of any filler, such as impregnated glass. .

The solution to the inventor's dilmer demonstrated the use of gas assist in plastic injection molding of the headlight cover. However, the design did not allow gas in the plastic-defining cavity to form a hollow or channel in the gas-finished part. The substantially flat portion of the headlight cover was required to have a continuous cross-sectional thickness, and the appearance of gas channels as well as the possibility of gas penetration outside the channels was difficult to accept in customer specified component designs. Furthermore, after a series of attempts to design headlight cover operations with gas channels in selected locations, the emergence of gas channels may impair the mechanical strength of the cover, especially in the line as a component of the coupling of the flange arm to the cover plate. Found. So the inventor's solution turned to a new form of the gas assisted plastic injection molding process, which is just outlined.

[Initiation of invention]

The present invention provides a plastic injection molding process that utilizes a first fill of pressurized gas to assist molding in the molding space, but no first fill of gas enters the molding space. In this application, a first fill of gas is selected to be sufficient and pressured to be injected into the mold and to enter a volume substantially adjacent to the molding space to help fill the molding space with molten resin.

Molten plastics can be injected into the plastics at pressures that do not reduce the molecular level of stress. The pressure of the volume of gas adjacent to the forming space allows for direct and regulated pressure application to the flowable resin in the forming space. The gas assist thereby adjusts the quality of the surface by maintaining intimate contact of the resin with the mold walls constituting the molding space while hindering resin cooling, i.e. shrinking of the resin. It is also an advantage of the process of the invention that the specific pressure and / or exclusion of the gas pressure of the mold do not affect the plastic in the molding space. Introduction of the gas can be accompanied by various means well known in the art.

The substantially adjacent volume containing gas may be a rnner in the mold, and the exclusion step may be achieved by separating the mold powder and causing the melt to rupture. Instead, the turbidity may be sewn, cut or opened by similar mechanical manipulations to depressurize the pressure in the mold, or by other means well known in the art. A second charge of pressurized gas can be introduced into the mold at a remote location from the first resin flow passage that allows the resin to enter the molding space. The second filling of the gas is of sufficient pressure and amount to enter the forming space but not into the first resin flow passage. In the embodiments of FIGS. 9 and 10, a second fill of gas is drawn directly into the forming space. In the embodiment of FIGS. 4-8, the second filling of gas is led into the resin reservoir in communication with the forming space by the second resin flow passage. Instead, when drawn into the resin reservoir, the second filling of gas is of sufficient pressure and amount to enter the resin reservoir and the second resin flow passage but not into the internal space of the molding die.

Further objects and features of the present invention will become apparent from the following description of the best mode for carrying out the invention.

Best Mode for Carrying Out the Invention

Figure 1 shows the normal sequence of steps involved in practicing the method of the present invention. 2 is a schematic illustration of an exemplary full-length molding, in which a lens cover, precursored to the form referred to in the ongoing discussion, is generally indicated at 20. The following description of the invention will be made in connection with the corresponding step of FIG. 1 the method steps of FIG. 1 for ease of explanation. As described in the preamble, the general principle of injection molding of gas assisted injection molding is disclosed in United States Patent No. 4,101,617, which is a basic patent granted to Friedrich on 18 July 1978. The present invention is directed to the production of products with good surface quality on a commercial basis, which controls the introduction of molten plastic and pressurized gas into the mold on repeatable soils and then distributes the interior of the hollow molded article. It is an improvement based on the Friedrich presentation of the basic problem. Referring to FIG. 1, in step 10, the molten plastic resin is injected into the injection hole of the mold of the injection molding apparatus. In the application of FIG. 2, the amount of resin is sufficient to fill the space for forming the mold and the portion of the volume defined by the mouth opening 24 and the mouth 26 of the mold 20. As shown in FIG. The tuyere 24 and the tudo 26 help to define a first resin flow passage extending between the injection hole and the molding space.

In this case, the molding space is a volume that is light on reference line "A", which defines the shape of the finished article. The finished article is a headlamp lens cover, generally indicated at 22. The cover 22 consists of a substantially flat plate 30 having a thick transverse peripheral frame 32. A pair of mounting flanges 34a and 34b are integrally attached to the opposite transverse ends of the plate 30 by respective webs 36a and 36b. The central portion of the mounting flanges 34a and 34b includes notches 38a and 38b, which are shaped to mate with the actuator arm on the servo mechanism that will lens the lens 22 between its open and closed positions.

The outer surface of the flat plate 30 must be free of bonding to meet automotive company standards as a Class A surface is finished. In addition, the plate must be free of bends or deformations over its surface area to ensure proper fit and appearance when assembled into the vehicle.

Mounting flanges 34a and 34b should be integrally joined to plate 30 in a true jperpendicular relation. The deviation from the true relationship is inclined from the proper mechanical coupling of the mounting flanges 34a and 34b to the actuator arm to the headlamp lens cover 22. Furthermore, the mounting flanges 34a and 34b should have a suitably strong mechanical connection to the plate 30 through the webs 36a and 36b.

Thus, in step 10, the filling of the plastic resin is sufficient to nominally fill the molding space without any gas entry into the molding space, but during the removal of the product from the mold space or during subsequent thermal cycling of the product. It is injected at a pressure that is not large enough to induce microscopy adaptability in the plastic, which causes it. The temperature of the plastic filling is within the range of processing temperatures for the resin composition to ensure sufficient fluidity of the plastic filling. However, the plastic injection temperature is not so great as to cause the resulting weakening of the material, including shearing or burning of the resin composition, and the resulting weakening of the material and inhomogeneity due to separation of the packing. .

In step 12, a first charge of pressurized gas is injected into the injection hole through the spout 24. However, the filling of the gas is selected to be of sufficient pressure and amount to avoid entry of the gas into the forming space. The volume at which gas is available is shown schematically at (28). The definite pressure and amount of gas required should be determined in relation to the criteria for one product through repeated test procedures in the normal test process. In the case of the headlight lens cover 22, the waterway 25 is shaped to receive a substantial amount of pressurized gas to aid in shaping and fixing. As shown in FIG. 3, the waterway 26 may have a bulbous cross section, that is, a shape of inverted water droplets to some extent to encourage particles of gas from the forming space to the waterway and the containment vessel. The presence of pressurized gas in the volume indicated at 28 helps to fill the molding space with molten resin, thereby avoiding the need for a relatively high plastic injection pressure. In step 14, the pressurized gas is retained in the volume 28 while the plastic solidifies in the forming space. The presence of pressurized gas during solidification promotes intimate contact with the walls of the molding space of the plastic to improve surface quality. Gas pressure counteracts the conventional tendency of plastics to cool while leaving grooves in the surface of finished products.

In step 16, the molding 20 is depressurized by excluding the pressure in the molding 20 and the finished product is removed. Pressure exclusion can be caused by separation of the mold dividing and magnetic rupture of the tap 26. For example, in some form of gas assisted molding process, the interior of the molding is excluded through a gas recovery step comprising a tire, a valve and a storage tank. In this case, the ballway 26 has a bulbous cross-sectional shape leading to magnetic rupture in the separation of the mold powder.

Instead, the molding 20 may be depressurized by perforation, shearing or mechanical action applied to the tumbler 24 or tumbler 26 prior to separation of the mold dust or by nozzle retraction.

In the reduced or excluded state of molding, the coagulation molding 20 is removed from the mold. The appendages of the trough 26 and trough 28 may be separated from the finished product in accordance with conventional work. A description will now be made with reference to FIGS. 4 to 10. The second filling of pressurized gas can be led into the mold at a location remote from the first resin flow passage that allows the resin to enter the molding space. The second filling of the gas is of sufficient pressure and amount to enter the forming space but not into the first resin flow passage. As shown in Figs. 4 to 8, the second filling of the gas is led into the resin reservoir 40 in communication with the molding space by the second resin flow passage. Instead, when drawn into the resin reservoir 40, the second filling of gas is of sufficient pressure and amount to enter the resin reservoir 40 and the resin flow passage but not into the molding space. The first and second filling of pressurized gas are drawn into the mold substantially simultaneously with forming a single article 22 '. Parts having a structure or function similar to those of the first to third parts are given a single fundamental designation, whereas in FIGS. 9 and 10 the components are given a dual fundamental designation. The resin reservoir or spillover 40 is in communication with the forming space defining the plastic product produced. The resin reservoir 40 assists in the configuration of the second resin flow passage extending from the molding space, and causes the molten plastic resin to flow from the resin tank 40 therefrom.

As best shown in FIG. 5, a second fill of gas is drawn into the lid 23 of the article 22 ′ through the detachable gas pin 2 shown at its gas injection position. . The gas preferably flows through the fins 25 into the resin reservoir 40 and along the second resin flow passage. The gas is of sufficient pressure and amount to enter the second resin flow passage and from there into the forming space but not into the first resin flow passage.

Instead, it may not be required for a second fill of gas to enter the forming space (because of its appearance and size). In such a case, it only enters the second resin flow passage since the pressure and amount of the second charge of the gas are adjusted. 8 illustrates the gas pin in the retracted position to allow gas pressure to withdraw the article 22 '. 9 and 10 show a modified detachable (gas pin 25) with a modified for direct injection of a second fill of pressurized gas into a thick portion 23 '(such as thick portion 23) of a plastic article 22 ". Gas pins 25 'are illustrated in Fig. 9. In Fig. 9, pin 25' extends into thick portion 23 'while in Fig. 10 pin 25' removes molding. The second filling of the gas is of a pressure and amount that enters the forming space but not into the first resin flow passage that causes the molten resin plastic to enter the forming space. It is to be understood that the terminology described and illustrated herein is intended to be in the nature of words of description rather than of limitation, and obviously, the invention is capable of many modifications and variations in light of the above teachings. It is to be understood that the invention may be practiced otherwise than as specifically described in the appended claims.

Claims (26)

A method of using gas assist in molding a plastic product in an injection molding apparatus comprising a mold having an injection hole, the method comprising; Injecting an amount of molten plastic resin sufficient for preparation of the plastic product according to the resin flow passage extending through the injection hole and from the rising hole to the molding space in the mold; Injection of a pressurized gas into the mold so that the gas filling enters the resin flow passage but not enough pressure and amount into the molding space; Maintaining gas filling in the mold under pressure in which the plastic resin solidifies in the forming space; And releasing the gas pressure in the resin flow passage. 2. The method of claim 1, wherein the step of releasing the molding consists of separation of the mold dividing of the mold to cause magnetic bursting of the plastic resin containing pressurized gas in the resin flow passage. 2. The method of claim 1 wherein the step of releasing the molding includes the step of opening the resin flow passage. 4. The method of claim 3, wherein the step of opening comprises stitching the plastic resin. 4. The method of claim 3 wherein the step of opening comprises shearing the plastic resin. CLAIMS 1. A method of injection molding a plastic product having at least one actual planar portion in an injection molding apparatus comprising a mold having an injection hole, the method comprising: A molten plastic sufficient for the preparation of the plastic product according to the resin flow passage which includes a portion extending through the injection hole and from the injection hole to the molding space in the mold and substantially accessing the portion of the molding space corresponding to the planar portion. Injecting the amount of resin; Injecting the filling of pressurized gas into the mold to a sufficient pressure and amount so that the filling of gas enters into the access portion of the resin flow passage which accesses the forming interior space corresponding to the planar portion, but not into the forming space; Maintaining gas filling under pressure in the access portion while the plastic resin solidifies in the forming space; And releasing the gas pressure in the access portion prior to withdrawing the plastic article from the mold. 7. The method of claim 6, wherein the step of releasing the molding includes separating the mold mold powder of the mold, causing the portion of the resin flow passage to self-rupture to approach a portion of the forming space that substantially corresponds to the planar portion. 7. The method of claim 6 wherein the step of releasing the molding includes opening a resin flow passage that accesses a portion of the forming space that substantially constitutes a planar portion. 9. The method of claim 8, wherein the step of opening comprises the step of stitching the plastic resin. 10. The method of claim 8, wherein the step of opening comprises shearing the plastic resin. A method of using gas assist in molding a plastic product in an injection molding apparatus comprising a mold having an injection hole and a molding space, the method comprising; Injecting an amount of molten plastic resin sufficient to prepare a plastic product according to the resin flow passage extending through the injection hole and from the injection hole to the molding space in the mold; Injecting the first filling of the pressurized gas into the mold so that the first filling enters the resin flow passage but not into the molding space so as to have a sufficient pressure and amount; Injecting a second charge of the pressurized gas into a mold at a position remote from the resin flow passage so that the second charge of the gas enters the forming space but not into the resin flow passage to a sufficient pressure and amount; Maintaining the first and second gas charges in the room under pressure while the plastic resin solidifies in the forming space to complete the formation of the plastic product; And releasing the gas pressure in the resin flow passage and in the forming space. 12. The method of claim 11, wherein the step of releasing the resin flow passage consists of separation of the two powders of the mold to cause magnetic rupture of the plastic resin containing pressurized gas into the resin flow passage. 12. The method of claim 11, wherein releasing the resin flow passage comprises opening the resin flow passage. 14. The method of claim 13, wherein the step of opening comprises stitching the resin. The method of claim 13 wherein the step of opening comprises shearing the plastic resin. 12. The method of claim 11, wherein the second charge of pressurized gas is directly injected into the forming space. An injection molding method of a plastic product in an injection molding apparatus comprising a mold having a resin reservoir in communication with an injection hole, a molding space, and a molding space, the method comprising: a method; According to the first resin flow passage extending from the injection hole to the molding space through the injection hole and the second resin flow passage extending from the molding space to the resin storage tank, the molten plastic resin is sufficient to prepare the plastic product. Injection of the sheep; Injecting the first filling of the pressurized gas into the mold so that the first filling enters the first resin flow passage but not into the forming space; Sufficient pressure and volume is sufficient to allow a second charge of the injection gas into the resin reservoir, the second charge of gas enters into and out of the second resin flow passage and into the forming space therein, but not in the first resin flow passage. Injection molding Maintaining the first second gas charge in the mold under pressure while the plastic resin solidifies in the forming space to complete the formation of the plastic product; And releasing the gas pressure in the first resin flow passage and in the forming internal space prior to withdrawing the plastic product from the mold. 18. The method of claim 17, wherein the step of releasing the first resin flow passage comprises removing the plastic powder containing the pressurized gas in the first resin flow passage portion of the molding space including separating the two powders of the mold. How to burst. 18. The method of claim 17, wherein the step of releasing the molding comprises the step of opening the first resin flow passage. 20. The method of claim 19, wherein the step of opening comprises the step of plastic stitching. 20. The method of claim 19, wherein the step of opening comprises shearing the plastic resin. An injection molding method of a plastic product in an injection molding apparatus comprising a mold having a resin reservoir in communication with an injection hole, a molding space, and a molding space, the method comprising: a method; According to the first resin flow passage extending from the injection hole to the molding space through the injection hole and the second resin flow passage extending from the molding space to the resin storage, the molten plastic is sufficient to prepare the plastic product. Injection of the sheep; Injecting the first filling of pressurized gas into the mold such that the pressure and amount are sufficient to allow the first filling to enter the first resin flow passage but not into the molding space; Injecting a second filling of pressurized gas into the resin reservoir to a pressure and amount sufficient to allow the second filling of gas to enter the second resin flow passage but not into the molding space; Injecting a second filling of pressurized gas into the resin reservoir so that the pressure and amount are sufficient to allow the second filling of gas to enter the second resin flow passage but not into the molding space; Maintaining the first and second gas charges in the mold under pressure while the plastic resin solidifies in the forming space to complete the formation of the plastic product; And releasing the gas pressure in the first and second resin flow passages prior to removing the plastic product from the mold. 23. The method of claim 22, wherein the step of releasing the first resin flow passage comprises the step of separating the two powders of the run, wherein the plastic resin contained in the first gas flow passage of the molding internal space is magnetically ruptured. How to. 23. The method of claim 22 wherein the step of releasing the molding comprises the step of opening the first resin flow passage to allow the gas contained therein to flow. 25. The method of claim 24, wherein the step of opening comprises stitching the resin. 25. The method of claim 24, wherein the step of opening comprises shearing the plastic resin to circulate gas contained therein.